Ownership Interests in and Advances to Partner Companies and Funds - Narrative (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended										3 Months Ended			5 Months Ended	12 Months Ended
	Jul. 31, 2016	Jun. 30, 2016	Apr. 30, 2016	Jan. 31, 2016	Jul. 31, 2015	Apr. 30, 2015	May 31, 2014	Apr. 30, 2014	Feb. 28, 2014	Jan. 31, 2014	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Jul. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investment [Line Items]
Proceeds from sale of business															$ 73,965	$ 25,058	$ 82,822
Adjusted carrying value of capital											$ 151,840				154,666	151,840
Equity method investment assets exceed carrying value of investment															119,000
Initial Revenue Stage [Member] | Maximum [Member]
Investment [Line Items]
Revenue stage threshold															5,000
Expansion Stage [Member] | Maximum [Member]
Investment [Line Items]
Revenue stage threshold															20,000
Expansion Stage [Member] | Minimum [Member]
Investment [Line Items]
Revenue stage threshold															5,000
High Traction Stage [Member] | Minimum [Member]
Investment [Line Items]
Revenue stage threshold															20,000
Goodwill [Member]
Investment [Line Items]
Equity method investment allocation of excess fair value															20,800
Intangible Assets [Member]
Investment [Line Items]
Equity method investment allocation of excess fair value															98,200
Putney, Inc. [Member]
Investment [Line Items]
Proceeds from sale of business			$ 58,600
Gain on sale of business			55,600
Amount held in escrow			600
Thing Worx Inc [Member]
Investment [Line Items]
Proceeds from sale of business			3,300	$ 4,100	$ 3,300
Gain on sale of business			3,300	$ 4,100	3,300
Alverix Inc [Member]
Investment [Line Items]
Proceeds from sale of business					1,700					$ 15,700
Gain on sale of business					1,700					$ 15,700
Crescendo [Member]
Investment [Line Items]
Proceeds from sale of business									$ 38,400					$ 2,900
Gain on sale of business														$ 2,900		2,914
Cost-method Investments, realized gains									27,400								27,365
Quantia [Member]
Investment [Line Items]
Proceeds from sale of business					$ 7,800
Asset impairment charges												$ 2,900
Quantia Inc. [Member]
Investment [Line Items]
Proceeds from sale of business	$ 600
Gain on sale of business	$ 600
DriveFactor Inc. [Member]
Investment [Line Items]
Proceeds from sale of business			1,100			$ 9,100
Gain on sale of business			$ 1,100			$ 6,100
InfoBionic [Member]
Investment [Line Items]
Asset impairment charges												$ 3,200
Dabo [Member]
Investment [Line Items]
Asset impairment charges													$ 2,300			$ 2,356
Sotera [Member]
Investment [Line Items]
Proceeds from sale of business							$ 4,200	$ 4,200
Cost-method Investments, realized gains								$ 1,500									1,453
Nupathe [Member]
Investment [Line Items]
Proceeds from sale of business									23,100
Gain on sale of business									$ 3,000								3,017
Proceeds from divestiture of businesses and interests in affiliates (in dollars per share)									$ 3.65
Appfirst [Member]
Investment [Line Items]
Proceeds from sale of business		$ 900
Asset impairment charges											$ 3,600				1,700
Bridgevine Inc [Member]
Investment [Line Items]
Proceeds from sale of business		5,000
Gain on sale of business		$ 400													424
Aventura [Member]
Investment [Line Items]
Asset impairment charges															3,600
Adjusted carrying value of capital															0
Penn Mezzanine Assets [Member]
Investment [Line Items]
Asset impairment charges															2,360		$ 255
Other Assets															$ 200